The methods of repairing existing underground pipes heretofore proposed are divided generally into those wherein a metal tubular material is used, and those using a plastic tubular material. From the viewpoint of the reliability of repairs, the methods of the former type are more excellent wherein the metal tubular material is used.
The methods of repairing existing underground pipes with the metal tubular material already proposed include the so-called pipe-in-pipe method wherein metal tubular members having a specified length and a circular cross section are inserted into the existing underground pipe while joining the tubular members to one another by welding within a work pit formed by excavation at an intermediate portion of the underground pipe to install a new metal pipe inside the underground pipe.
However, the pipe-in-pipe method is not desirable because this method requires much labor and time for welding the metal tubular members to one another, is low in work efficiency and necessitates a wide work space, i.e., a work pit of increased size, for successively joining the tubular members by welding. Further if it is attempted to use this method for repairing sewage pipes, manholes are too small and unsuitable for use as work pits.